The Siebel Si 204 is a twin-engined transport-, trainer- and passenger-aircraft developed by the German manufacturer Siebel Flugzeugwerke. Production was performed by SNCAC, Société Nationale de Constructions Aéronautiques du Centre in France, by CKD (Ceskomoravská Kolben-Danek) / BMM (Böhmisch-Mährische Maschinenfabrik AG) and Aero in the Protectorate of Bohemia and Moravia (Czechoslovakia).

The wartime production of approx 1216 Si 204 was performed by Siebel (15 prototype aircraft), SNCAC (168), CSK/BMM (492) and Aero (541). The Post-War production was held by SNCAC (ca. 300) including NC.701 Martinet (Si 204 D Renault 12S) and NC.702 Martinet II (Si 204 A Renault 12S) and by Aero (180) including C-3A, C-3B and C-103 (Passenger-Version).